The present invention is directed to a novel procedure for the production of high surface area mixed metal oxides containing one or more small crystallite phases of the mixed metal oxides. In particular, the present invention is directed to a procedure for the production of high surface area mixed metal oxides possessing the perovskite crystalline structure.
Various literature references such as Gallagher, Materials Research Bulletin, Volume 3, pages 225-238, 1968; and Bonnet, et al., Bulletin Society Chime France, No. 5 & 6, pages 1062-1070, 1975; have reported simple techniques for the preparation of rare earth iron and cobalt mixed oxides produced from hexacyanometallates. The resulting mixed metal oxides disclosed in these references has been found to possess the perovskite crystalline structure. The general technique disclosed in each of these references is heating the starting hexacyanometallate compound material to temperatures greater than 1000.degree. C. in air or pure oxygen with a heating rate in excess of 100.degree. C. per hour to produce the mixed metal oxide possessing the perovskite structure. However, perovskites produced by this procedure are characterized as possessing extremely low surface areas on the order of 2m.sup.2 /gm.
In a recent article by Imai et al., Materials Research Bulletin, Volume 19, pages 1293-1300, 1984, the authors disclose the preparation of cobalt lanthanum oxide catalysts possessing the perovskite structure and having surface areas of between 11 to 50m.sup.2 gm. The procedure of Imai et al. includes taking a fine mist copmrising a mixed solution of the metal salts and a reagent such as ammonium chloride or polyvinyl alcohol and heat treating this mist to form particles. The particles were then fitted to produce the oxide. While the procedure of Imai et al improves the surface area of the resulting cobalt lanthanum oxide perovskite material by the formation of extremely fine particles, it is evident that it is quite complicated and clearly not economical. Applicants present invention is directed to a simple economical procedure for producing mixed metal oxides, in particular, high surface area mixed metal oxides possessing the perovskite crystalline structure.